📚 Gathering Evidence in A-Level Physics | A-Level物理实验数据收集
In CIE A-Level Physics, gathering evidence is more than taking readings; it means planning a fair test, choosing instruments with suitable precision, repeating measurements, recording data clearly, and estimating uncertainties so that conclusions are supported by reliable data.
在 CIE A-Level物理中，收集证据不仅仅是读取数值；它意味着设计公平实验、选择合适精度的仪器、重复测量、清晰记录数据并估算不确定度，使结论建立在可靠数据之上。
1. What Is Evidence in Experimental Physics? | 实验物理中的证据是什么？
Evidence means numerical data plus the conditions under which it was collected. A single reading is rarely convincing; a set of repeated values with known instrument precision and controlled variables is what allows a valid conclusion.
证据是指数值数据以及收集这些数据时的条件。单一读数很少具有说服力；只有已知仪器精度、控制变量条件下的重复数据才能支持有效结论。
In CIE practical papers, examiners look for whether you choose a sensible range, repeat readings, and record values to the correct number of significant figures.
在CIE实验考试中，考官关注你是否选择了合理的测量范围、是否重复读数、以及是否按正确有效数字记录数据。
2. Planning for Reliable Data | 规划可靠数据
Before taking any measurement, identify the independent variable, dependent variable, and control variables. The independent variable should be changed over a wide enough range to reveal a trend, while control variables must be kept constant or monitored.
在测量之前，先确定自变量、因变量和控制变量。自变量应在足够大的范围内变化以显示趋势，而控制变量必须保持恒定或被监测。
For example, when investigating the period of a pendulum, length is the independent variable, period is dependent, and mass, amplitude and air currents must be controlled. Using lengths from 0.200 m to 1.200 m gives better evidence than using only three close values.
例如，研究单摆周期时，摆长为自变量，周期为因变量，质量、振幅和气流需控制。使用0.200 m到1.200 m的摆长范围比只用三个接近的值能提供更好的证据。
A preliminary experiment helps identify a suitable range and the key difficulties, but in an examination you may need to state the range directly.
预实验有助于确定合适的范围和主要困难，但在考试中你可能需要直接说明测量范围。
3. Choosing Measuring Instruments | 选择测量仪器
The instrument must be precise enough for the quantity being measured, but using an unnecessarily precise instrument can waste time and may not improve accuracy if other errors dominate.
仪器必须对被测物理量足够精确，但使用不必要的精密仪器可能浪费时间，并且在其他误差占主导时可能无法提高准确度。
| Quantity | Suitable instrument | Typical precision |
|---|---|---|
| Length up to 1 m | metre rule | ±1 mm |
| Small thickness or wire diameter | micrometer screw gauge | ±0.01 mm |
| Internal or external diameter | vernier caliper | ±0.1 mm |
| Time interval | digital stopwatch | display ±0.01 s, but human reaction about ±0.2 s |
| Temperature | liquid-in-glass thermometer | ±0.5 °C |
| Current | digital ammeter | ±0.01 A, depending on range |
| Voltage | digital voltmeter | ±0.01 V, depending on range |
| Mass | electronic balance | ±0.01 g or ±0.001 g |
| Angle | protractor | ±1° |
Record the instrument precision in your data table; this is the smallest increment or half increment that you can reliably judge.
在数据表中记录仪器精度；这是你能可靠判断的最小分度或半分度。
Do not quote a result to more decimal places than the instrument allows. A micrometer reading of 3.45 mm should not become 3.4500 mm.
不要记录比仪器允许的小数位更多的结果。千分尺读数3.45 mm不应写成3.4500 mm。
4. Reducing Systematic Errors | 减少系统误差
Systematic errors shift all readings in the same direction, often because of zero error, parallax, a wrongly calibrated scale, or a constant external condition. They cannot be reduced by repeating.
系统误差使所有读数朝同一方向偏移，通常由零误差、视差、刻度校准错误或恒定的外部条件引起。重复测量不能减少系统误差。
Check zero readings before use. For a mass balance press tare, for an ammeter check that the needle reads zero when no current flows, and for a micrometer close the jaws and record the zero error.
使用前检查零读数。对于天平按归零键，对于电流表检查无电流时指针是否指零，对于千分尺闭合测砧并记录零误差。
Parallax is avoided by placing the eye perpendicular to the scale. Use a set square or align the pointer with its mirror image where possible.
通过将眼睛垂直于刻度放置来避免视差。可能时使用三角尺或使指针与其镜像重合。
5. Reducing Random Errors Through Repeats | 通过重复测量减少随机误差
Random errors cause readings to scatter around the true value. Repeating a measurement and finding the mean reduces their effect, and the spread of repeats gives an estimate of uncertainty.
随机误差使读数在真值附近波动。重复测量并取平均值可减小其影响，重复值的分散程度给出不确定度的估计。
For a quantity such as the diameter of a wire, measure at several different positions and orientations, then calculate the mean. For a pendulum period, measure the time for 10 oscillations and divide by 10; this reduces the impact of reaction time on a single period.
对于导线直径等量，在不同位置和方向测量多次，然后计算平均值。对于单摆周期，测量10次振荡的时间再除以10；这减少了反应时间对单个周期的影响。
Repeat readings should be taken without changing controlled variables. If conditions drift, record the new conditions rather than pretending they are constant.
重复读数应在控制变量不变的情况下进行。如果条件发生漂移，应记录新条件，而不是假装条件恒定。
6. Recording Data in Tables | 用表格记录数据
A good results table has clear headings with units and uncertainty. Write the quantity and unit in the heading, such as ‘Length L / m’, not just ‘L’. Each column should show values to a consistent number of decimal places.
良好的结果表应有清晰的表头，包括单位和不确定度。在表头中写出物理量和单位，例如“长度 L / m”，而不是只写“L”。每列数值的小数位数应保持一致。
Do not include your calculations in the raw data table; keep separate columns for processed quantities such as mean, squared values, or reciprocals. This makes your evidence easier to check.
不要在原始数据表中包含计算；将平均值、平方值或倒数等处理量放在单独的列中。这使你的证据更易于检查。
Record the number of readings taken, and if a reading has been repeated, list all repeats rather than only the final average.
记录所取读数的次数，如果某读数已重复，列出所有重复值而不仅仅是最终平均值。
7. Handling Anomalous Results | 处理异常结果
An anomalous result lies well outside the pattern of repeated readings. It should not be silently deleted; circle it, repeat the measurement if possible, and decide whether it is caused by a reading error or a real change in conditions.
异常结果远离重复读数的总体模式。不应默默删除；应圈出该结果，可能的话重新测量，并判断它是由读数错误还是条件的真实变化引起的。
If you exclude an anomalous point from an average, state that you have done so and give a reason. In a graph, the anomalous point can be plotted but ignored when drawing the line of best fit.
如果从平均值中排除异常点，应说明已排除并给出理由。在图中，异常点可以标出，但在绘制最佳拟合线时不予考虑。
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